Hard Blok Water Jacket Filler Is a Specially Formulated, Cement-Based Product With Refined, Size-Graded Iron Particles Combined At An Optimum Ratio To Provide Maximum Strength, Vibration Dampening, and Heat Dissipation Required In High Performance Race Engines. Its Coefficient Of Thermal Expansion Is Identical To Cast Iron Engine Blocks. Product Has Been Tested and Proven Effective In Aluminum Blocks. Remains Stable At All Operating Temperatures. Does Not Soften When Exposed To High Heat, Nor Erode Under Water.Fills The Smallest Spaces In The Water Jacket. Does Not Shrink Or Pull Away From The Cylinder Walls. Does Not Expand.Extends Cylinder Wall Life Both By Preventing Cracked Walls and By Causing The Walls To Wear Truer. Honing Is Minimized During Rebuilds.A Race-Proven Advantage Used By Winners In All Types Of Racing Since 1986.Non-Hazardous and Non-Corrosive. Contains No Toxic Material. Once Hard, It Cannot Be Removed From The Block.Notes: Block Castings Are Not Precise. One Side May Vary From The Other. Variance Between Blocks Can Be Considerable. H & H Is Not Responsible For This Variance. One Tall Fill Unit Will Fill Most Big Blocks To The Bottom Of The Water Pump Connection. In Certain Tall Deck Blocks, The Fill Level May Be An Inch Or So Lower. This Level Is Adequate To Stiffen The Cylinder Walls.Pit Stop USA offers Hard Blok Engine Block Filler - Short Fill - (2) 6-1/4 lb. Bags 860212 at low everyday prices. Be sure to check out all of our products from Hard Blok including Hard Blok Engine Block Filler.